Molester's Train: Keiko's Hips (1983)

Perverted detective Ippei seizes an opportunity to win after repeatedly losing at Sudo's gambling den, but a thug barges in and steals about 10 million yen of the den's money. The thug is Shozo. He goes to a hotel with his mistress Keiko and they get into a fight, but Keiko strangles Shozo to death and steals his money. The whole incident is recorded on video in the room.